1. Technical Field
The present invention relates to a method and apparatus for is detecting the internal electric state of an in-vehicle secondary battery.
2. Related Art
In recent years, a second battery (rechargeable battery) mounted in a vehicle has been increased in its capacity so as to meet an increase in the amount of electrical loads mounted in the vehicle. Hence, avoiding the overcharge and over-discharge of the in-vehicle secondary battery has become very significant in these years. It is thus necessary to detect reliably and accurately information indicating the internal electric state of the second battery, which information includes information about a residual charged capacity of the secondary battery.
In such a circumstance, Japanese Patent No. 3249788 discloses a conventional technique to estimate information indicating the internal electric state of an in-vehicle secondary battery. The estimation technique proposed by this publication uses a discharge current change so characteristic related to waveforms of changes in the discharge current immediately before the constant-voltage charge of the battery. Hereinafter, this change characteristic is referred to as a “charge current approximation function.” This charge current approximation function is used to estimate a timing (estimated timing) at which the charge current reaches a given final value, and a capacity to be charged (charged capacity) until gaining the final charge current and a time necessary for the charge are calculated.
However, in the case of the forgoing technique, the charge current approximation function to be estimated is affected (i.e., fluctuated) by irregularities in the polarized state of the battery, resulting in that the function is deviated from the actual charge current waveform. Hence, in most cases, there is a large difference between a timing at which the actual charge current reaches the given value (i.e., actual timing) and the estimated timing. This results in that the accuracy of the charge capacity and the time necessary for the charge, calculated based on the foregoing estimating timing, becomes low.
In addition, in the case of the technique proposed by the foregoing publication, the charge current characteristic is estimated without considering influence resulting from differences of the charge efficiency of a battery. Hence, in particular, in an end period of the charge action, the charge current approximation function is obliged to have a lower accuracy. The estimation accuracy of the charged capacity and the time necessary for the charge is reduced.